In a laminate used as a packaging material, etc., a thermoplastic resin is used for the sealant layer. In particular, a polyethylene resin, a polypropylene resin and so on are used as the thermoplastic resin, from the viewpoint of being excellent in lamination processability and heat-sealing property.
However, while these resins can achieve high adhesion strength in heat sealing, they tend to adsorb components contained in foods, medicines, etc. Therefore, a package including a sealant layer made of such a resin so as to be adjacent to a space for containing contents is liable to deteriorate or degrade the contents.
For this reason, polyacrylonitrile resin (PAN), which is a non-adsorbing material, has been used for sealant layers in laminates used for packaging of foods and medicines. However, it is difficult to procure polyacrylonitrile resin films stably, and there is a need to find substitute materials for polyacrylonitrile resins.
Jpn. Pat. Appln. KOKAI Publication No. 2008-207823 describes a packaging bag which has high-speed-filling packaging applicability and has extremely low adsorption of volatile components derived from the contents contained in the bag. This packaging bag is made of a laminate material in which a base material layer, a low density polyethylene resin layer, and a cyclic polyolefin resin composition layer are stacked in this order. In this document, a structure is adopted in which a ratio of the thickness of the low density polyethylene resin layer to the thickness of the cyclic polyolefin resin composition layer is within the range of 20:1 to 2:1.
The invention described in Jpn. Pat. Appln. KOKAI Publication No. 2012-86876 aims to provide a packaging bag and a packaging container each having a sealant layer which is excellent in film-forming property, non-adsorbing property, and heat-sealing property. In order to achieve the above-mentioned object, this document describes that a laminate, which is composed of a base material layer, a linear low density polyethylene resin layer, and a cyclic polyolefin resin composition layer stacked in this order and the cyclic polyolefin resin composition has a predetermined composition, is used for a lid of a packaging bag or a packaging container. This invention uses a linear low density polyethylene resin and a cyclic polyolefin resin composition as the sealant layer.